This invention relates to a generating voltmeter and, more particularly, to a generating voltmeter that has a rapid response to changes in the voltage being measured.
A generating voltmeter is a device which uses a time-varying capacitance to measure d-c high voltages. In its basic form, the generating voltmeter comprises a motor-driven rotor that comprises one or more metal vanes at ground potential. When the rotor is rotated, it alternately covers and uncovers a stator that is connected to ground through a load resistance. When the rotating rotor and the stator are exposed to the electric field of a high voltage electrode located a short distance away, an alternating current flows through the stator and the load resistance to ground. This current is usually rectified and filtered to produce a d-c signal related in magnitude to the high voltage being measured.
The response time of such a basic generating voltmeter to voltage changes is limited by the speed of the rotor vanes. Ordinary generating voltmeters have a response time on the order of 100 milliseconds. This is much too slow to enable such a generating voltmeter to be used for controlling high voltage d-c power transmission systems. Precision resistors can be used for obtaining a suitable voltage measurement in such power systems, but such resistors are quite expensive and large.